Zhao Yongguo, Fu Xiaowen, Zou Zhi
College of Biology and Food Engineering, Guangdong University of Petrochemical Technology, Maoming 525000, China.
National Key Laboratory for Tropical Crop Breeding, Hainan Key Laboratory for Biosafety Monitoring and Molecular Breeding in Off-Season Reproduction Regions, Institute of Tropical Biosciences and Biotechnology of Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China.
Plants (Basel). 2024 Oct 19;13(20):2933. doi: 10.3390/plants13202933.
LEA_1 domain-containing proteins constitute a class of late-embryogenesis-abundant proteins that are highly hydrophilic and predominantly accumulate in mature seeds. Though LEA_1 proteins have been proven to be essential for seed desiccation tolerance and longevity, little information is available on their roles in non-seed storage organs. In this study, a first genome-wide characterization of the gene family was conducted in tigernut ( L., Cyperaceae), whose underground tubers are desiccation tolerant with a moisture content of less than 6%. Five family members identified in tigernut are comparative to four to six found in seven other Cyperaceae plants, but relatively more than three reported in Arabidopsis. Further comparison of 125 members from 29 plant species supports early divergence of the family into two phylogenetic groups before angiosperm radiation, and gene expansion in tigernut was contributed by whole-genome duplications occurring after the split with the eudicot clade. These two phylogenetic groups could be further divided into six orthogroups in the momocot clade, five of which are present in tigernut and the remaining one is Poaceae specific. Frequent structural variation and expression divergence of paralogs were also observed. Significantly, in contrast to seed-preferential expression of genes in Arabidopsis, rice, and maize, transcriptional profiling and qRT-PCR analysis revealed that genes have evolved to predominantly express in tubers, exhibiting a seed desiccation-like accumulation during tuber development. Moreover, transcripts in tubers were shown to be considerably more than that of their orthologs in purple nutsedge, another Cyperaceae plant producing desiccation-sensitive tubers. These results imply species-specific activation and key roles of genes in the acquisition of desiccation tolerance of tigernut tubers as observed in orthodox seeds. Our findings not only improve the understanding of lineage-specific evolution of the family, but also provide valuable information for further functional analysis and genetic improvement in tigernut.
含LEA_1结构域的蛋白质构成了一类晚期胚胎发生丰富蛋白，这类蛋白具有高度亲水性，主要积累在成熟种子中。尽管LEA_1蛋白已被证明对种子脱水耐受性和寿命至关重要，但关于它们在非种子贮藏器官中的作用却知之甚少。在本研究中，对莎草科的虎坚果（Cyperus esculentus L.）进行了该基因家族的首次全基因组特征分析，其地下块茎具有脱水耐受性，含水量低于6%。在虎坚果中鉴定出的5个家族成员与其他7种莎草科植物中发现的4至6个成员相当，但比拟南芥中报道的3个相对更多。对来自29种植物的125个成员的进一步比较支持了该家族在被子植物辐射之前早早就分化为两个系统发育组，并且虎坚果中的基因扩张是由与真双子叶植物分支分裂后发生的全基因组重复导致的。这两个系统发育组在单子叶植物分支中可进一步分为6个直系同源组，其中5个存在于虎坚果中，其余1个是禾本科特有的。还观察到旁系同源物频繁的结构变异和表达差异。值得注意的是，与拟南芥、水稻和玉米中LEA_1基因的种子优先表达不同，转录谱分析和qRT-PCR分析表明，LEA_1基因已进化为主要在块茎中表达，在块茎发育过程中表现出类似种子脱水的积累。此外，块茎中的LEA_1转录本显示比另一种产生对脱水敏感块茎的莎草科植物紫花莎草中的直系同源物多得多。这些结果表明，如在传统种子中观察到的那样，LEA_1基因在虎坚果块茎脱水耐受性的获得中具有物种特异性激活和关键作用。我们的研究结果不仅增进了对LEA_1家族谱系特异性进化的理解，也为虎坚果的进一步功能分析和遗传改良提供了有价值的信息。
